Datasheet

AD7796/AD7797
Rev. A | Page 23 of 24
APPLICATIONS
The AD7796/AD7797 offer a high resolution analog-to-digital
function. Because the analog-to-digital function is provided by
a Σ-Δ architecture, the parts are more immune to noisy
environments, making them ideal for use in sensor
measurement, and industrial and process-control applications.
WEIGH SCALES
Figure 17 shows the AD7796/AD7797 being used in a weigh
scale application. The load cell is arranged in a bridge network
and gives a differential output voltage between its OUT+ and
OUT– terminals. Assuming a 5 V excitation voltage, the full-
scale output range from the transducer is 10 mV when the
sensitivity is 2 mV/V. The excitation voltage for the bridge can
be used to directly provide the reference for the ADC because
the reference input range includes the supply voltage. This
allows a ratiometric measurement. Therefore, variations of the
excitation voltage do not affect the measurement.
The on-chip temperature sensor can be used for temperature
compensation of the bridge so the variation of the sensor
resistance with temperature drift can be monitored and the
conversions from the bridge can be compensated.
AD7796/AD7797
AIN(+)
AIN(–)
INTERNAL
CLOCK
AV
DD
DV
DD
REFIN(–)
REFIN(+)
DOUT/RDY
DIN
SCLK
MUX
GND
GND
CLK
Σ-Δ
ADC
V
DD
V
DD
×128
TEMP
SENSOR
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CS
IN+
IN–
OUT–
OUT+
06083-017
Figure 17. Weigh Scales Using the AD7796/AD7797